Oxidation Processes in Water Treatment: Are We on Track

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Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX

Oxidation Processes in Water Treatment: Are We on Track? Urs von Gunten*,†,‡,§ †

Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, 8600 Duebendorf, Switzerland School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL), 1015, Lausanne, Switzerland § Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, 8092 Zurich, Switzerland ‡

S Supporting Information *

ABSTRACT: Chemical oxidants have been applied in water treatment for more than a century, first as disinfectants and later to abate inorganic and organic contaminants. The challenge of oxidative abatement of organic micropollutants is the formation of transformation products with unknown (eco)toxicological consequences. Four aspects need to be considered for oxidative micropollutant abatement: (i) Reaction kinetics, controlling the efficiency of the process, (ii) mechanisms of transformation product formation, (iii) extent of formation of disinfection byproducts from the matrix, (iv) oxidation induced biological effects, resulting from transformation products and/or disinfection byproducts. It is impossible to test all the thousands of organic micropollutants in the urban water cycle experimentally to assess potential adverse outcomes of an oxidation. Rather, we need multidisciplinary and automated knowledge-based systems, which couple predictions of kinetics, transformation and disinfection byproducts and their toxicological consequences to assess the overall benefits of oxidation processes. A wide range of oxidation processes has been developed in the last decades with a recent focus on novel electricity-driven oxidation processes. To evaluate these processes, they have to be compared to established benchmark ozone- and UV-based oxidation processes by considering the energy demands, economics, the feasibilty, and the integration into future water treatment systems.

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INTRODUCTION

The trade-off between disinfection and DBP formation (i.e., between acute and chronic toxicity) has to be carefully evaluated.6,8 Generally, disinfection has the highest priority and should not be compromised by the control of DBPs.18 Nevertheless, in some countries, the use of chlorine and/or chemical disinfection in distribution systems has been entirely discontinued to avoid public health consequences and chlorineinduced taste and odor problems.19,20 Such changes require a very rigorous approach focusing on water resources protection, natural attenuation, multibarrier treatment, and careful maintenance of distribution systems.21

At the beginning of the 20th century, chemical oxidants (e.g., chlorine, ozone) were introduced in municipal water treatment for disinfection in industrialized countries, which are the focus of this paper.1,2 The combination of chemical disinfection with sand filtration led to a dramatic decrease of waterborne diseases.1 Though, this was recognized as a major advance, the detection of the disinfection byproduct (DBP) chloroform in the mid-1970s3,4 followed by the discovery of hundreds of other halogenated DBPs formed during chlorination and the potential link between DBPs and bladder cancer or miscarriages5 led to substantial changes in water treatment practices. DBPs are formed from the reactions of chemical oxidants with matrix components such as the dissolved organic matter (DOM), bromide and iodide.6−8 During ozonation, DBPs such as bromate9 and oxygen-rich compounds such as aldehydes, ketones and carboxylic acids are formed from reactions with bromide or DOM, respectively.10−12 In response to concerns about DBPs, other disinfectants such as chloramine6 or chlorine dioxide13 were applied in distribution systems. This led to significantly lower THM formation, however, other DBPs such as N-nitrosodimethylamine (NDMA)14,15 or chlorite/chlorate,16,17 respectively, were formed. © XXXX American Chemical Society

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OXIDATIVE ABATEMENT OF ORGANIC MICROPOLLUTANTS Range of oxidation processes. Almost in parallel to chemical disinfection, oxidative control of aesthetic parameters such as iron(II) and Mn(II),22−24 color and taste and odor25 and other inorganic contaminants (sulfide, nitrite and ammonia) was implemented in water treatment.26−28 Later on, oxidative treatment was applied for abatement of synthetic organic compounds (micropollutants) due to their widespread detection in drinking water sources.5,29,30 Received: January 30, 2018

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DOI: 10.1021/acs.est.8b00586 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

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Environmental Science & Technology

upgraded to use the O3/H2O2 process in the late 1990s as a means of treating atrazine and other herbicides. 72−74 Subsequently, the O3/H2O2 process was banned in France for treatment of source waters containing pesticides; today it is only approved in France for the treatment of chlorinated compounds.75 After this caesura, more research efforts were dedicated to the identification of transformation products from common contaminants (e.g., atrazine, methyl tert-butyl ether, dioxane) and model compounds to provide insights into oxidative reaction mechanisms.76−82 Transformation Products and Effects. The number of studies on the formation of oxidative transformation products increased significantly in the early 2000s concomitantly with the development of analytical methods such as liquid chromatography (LC) coupled with high resolution mass spectrometry.5,83 This resulted in a significant mechanistic knowledge gain for oxidation processes involving •OH84,85 and O3,27,86,87 which enabled the compilation of pathway prediction systems for transformation reactions induced by •OH88 and O3.89 Researchers also studied ferrate,51,90,91 chlorine,26,92−106 bromine,107,108 permanganate109 and chlorine dioxide,110−114 adding to the mechanistic understanding. This wealth of information triggered new worries about the formation of potentially toxic transformation products.115 Attempts to couple mechanistic information to toxicological consequences led to three major cases for transformation products that can be distinguished (Figure 2): Oxidative Treatment Leads to a Loss of the Primary Biological Activity Caused by the Parent Compound (Lower Red Curve in Figure 2). Numerous toxicological studies have demonstrated that the primary or secondary attack of an oxidant (most studies for O3 and/or •OH) on a target compound leads to a proportional loss of the primary biological effects for various classes of compounds such as antimicrobial agents,116−121 estrogenic compounds,122−124 herbicides125 and insecticides.126 The Transformation Products of Biologically Active Molecules Are (Potentially) Regulated Compounds with Higher Toxicity than the Parent Compound (Upper Red Curve in Figure 2). A case in point is the formation of chloroform during chlorination of triclosan, an antimicrobial agent.105,127 Even though in this case the antimicrobial activity of the target compound is lost, a new effect arises. This problem is even aggravated, by the photochemical formation of dioxins from chlorinated triclosan released to the aquatic environment.106 Another example is the formation of NDMA during chloramination of ranitidine-containing water.128,129 Formation of Toxic/Bioactive Compounds from Target Compounds with Low Biological Activity (Upper Red Curve in Figure 2). N,N-dimethylsulfamide, a nontoxic metabolite of the fungicide tolylfluanide, is transformed to the genotoxic Nnitrosodimethylamine (NDMA) during ozonation.130,131 NDMA was also formed during ozonation of secondary wastewater effluents containing antiyellowing agents.132 In another example the attack of •OH on quinoline led to an estrogenic compound, however, with a very low potency.133

Numerous chemical oxidants have been tested alone or in combination with adsorption (activated carbon) or tight membrane processes for an optimized abatement of micropollutants (Figure 1). The tested chemical oxidation processes include ozone (O3) and the corresponding advanced oxidation processes (AOPs), O3/H2O2, O3/UV to enhance hydroxyl radical (•OH) formation,27,31 ultraviolet light (UV) combined with H2O2 to produce •OH,32−34 permanganate,35,36 bisulfiteactivated permanganate,37,38 the (photo)-Fenton process,33,39 UV combined with S2O8− or HSO5− to produce sulfate radicals40−47 and their application for in situ chemical oxidation48,49 and ferrate(VI).50,51 A significant effort was made over decades to develop photocatalytic water treatment.52−55 However, some researchers were skeptical already at an early stage of investigations on TiO2-based photocatalysis, and also today there are only limited niche applications.56−59 Overall, in drinking water practice, most full-scale processes employ homogeneous ozone- or •OH-based processes due to their broadband action against many different classes of micropollutants,27,60 their maturity and/or relatively low energy demand, the controllable formation of DBPs and the relatively easy implementation at full-scale (Figure 1).2,32,61,62 From Kinetics to Transformation Products. In early applications of oxidation processes, most studies focused on the disappearance of target compounds.63−66 However, already during the development phase of oxidation processes, researchers recognized that typical chemical oxidant doses applied in water treatment do not yield full mineralization of most target compounds, but instead transformation products are formed.67−70 Despite the parallel research on disinfection byproduct formation, this fact was largely neglected until the new EU drinking water regulation in 1998 applied the same standard for pesticides and transformation products/metabolites.71 Especially in France, this came as an unpleasant surprise, because many drinking water treatment plants had been

Figure 1. Comparison of various chemical oxidants/processes for the abatement of micropollutants in municipal water treatment. Feasible processes are in the upper left corner (low DBP formation, oxidation of a broad range of micropollutants and a high feasibility (maturity and low energy demand). The arrows for chlorine dioxide and chlorine show that their feasibility is higher than shown in the picture, because they are widely applied in water treatment. Example how to read the graph: Mn(VII) has low formation of DBPs, a high feasibility (already widely applied in water treatment) but is a very selective oxidant, which does not warrant oxidation of a wide range of micropollutants.

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THE OXIDATION DILEMMA Oxidant Reactions with DOM. For simplicity, most mechanistic studies on contaminant oxidation are conducted in ultrapure water. However, under realistic conditions, the largest fraction of chemical oxidants is consumed by DOM (Figure 3).134−136 Much of this is due to oxidation of phenolic B


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N-oxides) are not removed in biological post-treatment after ozonation of a municipal wastewater effluent (Figure 2, horizontal dashed red lines).138 Nevertheless, it can be expected that ozone transformation products of aromatic compounds or olefins are more biodegradable than their parent compounds (Figure 2, descending dashed red lines).86 Bromide in Oxidative Water Treatment. Bromide plays a special role in oxidative water treatment because it can be oxidized to bromine, a reactive secondary oxidant, by some common oxidants.107 Bromine reacts with DOM to produce brominated byproducts (Br-DBPs), which are typically more toxic than the chlorinated analogues.151,152 If these Br-DBPs are formed, they are mostly recalcitrant during biological posttreatment (Figure 2, horizontal dashed blue line). For advanced oxidation processes such as O3/H2O2 or UV/H2O2, these DBPs are less important, because the transient bromine concentration is typically low and the bromine-reactive precursors are consumed by ozone and/or •OH. The major drawback for ozone-based treatment of bromide-containing waters is the formation of bromate,153 which is a possible human carcinogen with drinking water and ecotoxicological standards of 10 and 50 μg/L bromate, respectively.154,155 Bromate removal (e.g., by biological post-treatment) after its formation is not a viable option (Figure 2, dashed green line) and its formation has to be minimized/avoided as much as possible.9,27,153,154,156−164 Compared to conventional ozonation, the O3/H2O2 process leads to a significantly lower bromate formation.157 Trade-off between Energy Consumption and Bromate. In contrast to ozone-based processes, the UV/H2O2 process does not lead to bromate formation in bromide-containing waters (Supporting Information (SI) Figure S1).157,165 However, the energy consumption for the abatement of micropollutants to 10% of their initial concentrations, the electrical energy per order (EEO), is generally about 4−20 times higher (0.17−2.3 kWh/m3) for the UV/H2O2 process than for the O3/H2O2 process (0.04−0.25 kWh/m3).166,167 Therefore, there is a tradeoff between bromate formation and energy consumption, O3/ H2O2 is favored at lower and UV/H2O2 at higher bromide concentrations.168 If disinfection is an additional criteria, the UV/H2O2 process has a superior performance, because the high UV fluences for this AOP lead to an efficient inactivation of microorganisms (SI Figure S1).167 In contrast, only limited inactivation can be achieved by the O3/H2O2 process, because the ozone exposure is reduced due to its hydrogen peroxide induced decomposition to •OH, which is a weak disinfectant.27,169

Figure 2. Relative evolution of toxicity (human health) and/or biological effects during oxidative treatment of micropollutantcontaining waters as a function of the oxidant dose/exposure and the extent of biological post-treatment. MP: micropollutant; DOM: dissolved organic matter; TPs: Transformation products; DBPs: Disinfection byproducts; AOC: Assimilable organic carbon; BDOC: Biodegradable organic carbon.

moieties in DOM (1−2 mmol/gDOC, that is, μM DOMphenol concentrations).137 This is much higher than micropollutant concentrations of ≪0.1 μM in natural waters and wastewater effluents.30,138 The reaction of DOM with ozone and/or •OH leads to the formation of oxygen-rich byproducts (e.g., aldehydes, ketones and carboxylic acids) in total concentrations often >100 μg/ L,139,140 which is significantly above the sum of the concentrations of micropollutants (ca. 25 μg/L) detected in a wastewater treatment plant effluent after ozonation.138 Therefore, oxygen-rich byproducts may contribute more to the toxicity/biological effects of the treated water than micropollutants (Figure 2, blue line).141 Cases in point are the formation of toxic α,β-unsaturated enedials and oxoenals during UV treatment of phenols in presence or absence of H2O2 or the formation of quinones or catechols during ozonation.142−144 In line with the formation of such products, it has been observed that the toxicity to certain aquatic organisms increases after wastewater ozonation, with mostly an improvement after a biological treatment step (Figure 2, dashed blue line).141,145−147 Since these oxygen-rich byproducts are often easily biodegradable, a biological post-treatment step is routinely implemented after an oxidation/AOP in drinking water and wastewater effluents.11,138−141,148−150 So far, there is not sufficient information to assess the efficiency of biological post-treatment for transformation product abatement. However, it has been shown that various nitrogenous transformation products (e.g.,

Figure 3. Relative contribution of the various water solutes to the consumption of oxidants. The DOM is by far the major consumer of oxidants during water treatment, followed by bromide (and in some cases iodide) depending on their concentrations. Compared to these matrix components, micropollutants only contribute minimally to the oxidant consumption. Disinfection byproducts are formed from the reactions of oxidants with the matrix components, whereas the oxidation of micropollutants leads to transformation products. C


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chlorine,26 chlorine dioxide,206 bromine107 with organic micropollutants. In addition, several approaches, such as quantitative structure activity relationships (QSARs), quantum chemical computations (reactions with ozone or •OH) and the group contribution method (•OH) have been applied to predict second order rate constants for the reactions of organic compounds with oxidants.26,63,107,207−211 These empirical correlations yield predictions within a factor of 3 of the measured values,208 which is within the range of variation in measured second order rate constants from different laboratories.27 Prediction of Transformation Products. In addition to understanding the kinetics of compound abatement, the elucidation of transformation pathways for oxidative treatment of micropollutants is a tedious process involving labor-intense experiments with product analysis by various methods (e.g., GC-MS/MS, LC-MS/MS, NMR, etc.) (Figure 4a).27,76−78,85,86,108,110,114,117,212−224 Identification of the products of 10% of the 100 000 most common products in commerce145 could cost over 100 million USD for each oxidant assuming a very optimistic average time of 3 months per compound for a product study. This cost would be augmented by the thousands of new chemicals, which are registered every year.145 This theoretical exercise demonstrates that such a comprehensive screening is unlikely to occur. Instead, we need a prioritization and fundamental studies with model com-

AN UNEXPECTED REVIVAL OF OXIDATION PROCESSES WITH A SIGNIFICANT KNOWLEDGE GAIN Enhanced Wastewater Treatment. After a research and development phase of almost two decades,170−172 the Swiss authorities decided to upgrade about 15% of the country’s municipal wastewater treatment plants to reduce the load of organic micropollutants to the aquatic environment.173−177 This development was triggered by detection of pharmaceuticals, endocrine disruptors and personal care products in municipal wastewater effluents,178−182 combined with ecological studies suspecting/demonstrating the effect of endocrine disruptors on fish populations.183−187 In Germany and France similar approaches are currently being assessed.145,147,188−190 Overall, the European approach is guided by mostly ecological concerns, with an added benefit for drinking water, which is often abstracted from rivers (i.e., riverbank filtration) downstream of wastewater effluent discharges. Water Reuse. The recent increase in municipal water reuse is mainly driven by water security (e.g., Singapore191) and water scarcity in arid areas, which is often aggravated by climate change, population growth and competition for water resources with agriculture.192,193 A case in point is California, where water was initially recycled for industrial and agricultural purposes and then for drinking water production.194,195 Recently, a rigorous framework of multibarrier advanced water treatment systems was implemented to fulfill the criteria for direct water reuse and the surface water treatment rule.194,196−198 All of the suggested direct potable reuse treatment trains in California include an ozonation and/or UV/H2O2 process combined with pre- or post-treatment with reverse osmosis for disinfection and the abatement of micropollutants.194 Decentralized Systems. In the future, centralized municipal water systems may be partially replaced by more localized systems, due to the high cost of maintaining aging infrastructure of drinking water and wastewater networks as well as the rapid development of megacities. To support low maintenance water treatment in decentralized systems, electricity-based systems will likely prove to be advantageous both for disinfection and for oxidation of micropollutants.193,199−201 Finding the Needle in the Haystack. The Analytical Approach. The uncertainty about transformation products being formed during oxidation might become a barrier to these developments as already shown for the atrazine example above. The application of LC-high resolution MS-based analytical methods and data processing tools led to the detection of hundreds of micropollutants and their biological/oxidative transformation products in wastewater matrices.138,202−204 Currently, the interpretation of such data sets is very limited and we need a better connection to mechanistic studies and toxicity databases. The detection of new compounds often triggers kinetic and mechanistic studies of oxidation reactions of randomly selected micropollutants, which only leads to limited progress in the field. Rather, the emphasis should be on fundamental studies on selected functional groups, which are transferrable to micropollutants containing the same chemical moieties.27 Several promising approaches are discussed below. Prediction of Reaction Kinetics for Oxidation Reactions. The efficiency of an oxidative treatment depends directly on the reaction kinetics. There is already a large kinetic database for the reactions of various oxidants such as •OH,205 ozone,27

Figure 4. Two approaches dealing with large numbers of compounds during oxidation processes. (a) Experimental approach with kinetic and mechanistic studies, toxicological assessment and elucidation of problematic compounds by effect-driven analyses. (b) In silico assessment of micropollutants by prediction of transformation products and potential (eco)toxicological risks. For (b), experimental studies will only be performed with critical compounds. D


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UV-Based Processes. Vacuum UV (VUV, UV radiation 100 reaction rules.89 This allows an interpretation of results from nontarget analyses of oxidation processes229 and a rapid screening of possible transformation products for potentially toxic structures for, e.g., known carcinogenic groups (Figure 4b).230,231 There are numerous in silico prediction methods for mutagenicity, modes of action and ecotoxicity, which have been implemented in software packages.232−234 Only after a predicted compound is identified and suspected to cause a potential risk, it will be necessary to conduct laboratory studies on its formation, stability, fate and toxicity.

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SEARCHING FOR THE SILVER BULLET Future urban water systems may include both centralized and decentralized components with water reuse of e.g., gray water and concentrate streams.193 Whereas, centralized water systems will probably rely on well-established oxidation/disinfection methods, in decentralized systems (point-of-entry/use) electricity-based methods such as UV irradiation and electrochemical production of oxidants such as chlorine, hydrogen peroxide and ozone bear a huge potential because they are independent of the transport of chemicals.201,235−237 In recent years, the portfolio of chemical oxidation has been expanded to search for higher energy efficiency and lower DBP formation. Often, combined/hybrid processes are tested, however, an imperative comparison to the current benchmark oxidation processes ozonation, O3/H2O2 and UV/H2O2 is often missing. Ozone-Based Processes. Heterogeneous ozonation processes have been widely studied to enhance the transformation of ozone to hydroxyl radicals.238 A recently developed catalyst was efficient in reducing bromate formation with an efficient abatement of ozone-resistant micropollutants such as atrazine.239 However, the optimal concentration of the catalyst of 0.5 g/L (500g/m3) causes substantial problems related to the process design. The potential gain in efficiency is impaired by the problems related to heterogeneous processes, such as separation, fouling and deactivation of the catalyst, bleeding of potentially toxic elements and costs of the catalysts. Furthermore, natural and H2O2-induced ozone decomposition have hydroxyl radical yields of about 50%,27,240 wherefore, the margin for improvement is only about a factor of 2 if a process leads to 100% transformation of ozone to hydroxyl radical. Hence, the homogeneous O3/H2O2 process seems a more reasonable approach for bromate control by keeping the dissolved ozone concentration very low.241 To this end, optimized processes involving membranes (SI Figure S2a), multiple static mixers or multiple injection ports for ozone transfer to hydrogen peroxide-containing waters can be applied to warrant very low transient ozone concentrations leading to almost neglect bromate formation.241−243 Hydrogen peroxide can be produced electrochemically onsite and on demand as in the electro-peroxone process (SI Figure S2a),244 avoiding the transport of chemicals and enhancing the flexibility of the process. E


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Environmental Science & Technology disinfection, and to provide a residual disinfectant after treatment. In contrast, the oxidation of micropollutants by hydroxyl radicals and other reactive species formed on electrode surfaces, such as boron-doped diamond (BDD) electrodes, has low efficiency due to the diffusion limitations, competition with DOM and electrode surface limitation.267 In addition, costs and electrode stability are still an issue for BDDs. Plasma, Sonolysis, Natural and Synthetic Enzymes. Plasma-based and sonolysis processes have been studied for water treatment for several decades. Although they can oxidize contaminants,268 cost-effective applications seem to be far away or even impossible due to their high energy demand and significant up-scaling issues.33,269−272 Recently, ozone generators based on microplasma have become available and seem to be an attractive alternative at small-scale to conventional ozone generators.273 The application of natural and synthetic enzymes has been suggested as a sustainable option for water treatment.274,275 However, there are still limitations to these processes (see SI Text 1).

Research needs: The focus of further experimental research should be based on missing basic information related to functional groups and oxidants, which is applicable to whole classes of micropollutants. Improved workflows and data analysis for target and nontarget analyses are required and we need a better understanding of what is formed from the oxidation of micropollutants versus the organic matrix. Sensitive, robust, standardized and high throughput toxicological test systems with various human toxicological and ecotoxicological end points need to be developed. What Are the Implications of Oxidation of the Matrix Components? Due to the variability and complexity of natural or effluent DOM, the prediction of DBPs is still in its infancy. Research needs: Quantification of reactive functional groups in DOM for a better prediction of the efficiency of oxidation and of the formation of ensuing products. Which Is the Best Oxidative Treatment Option? Based on the complexity of oxidation processes, there is a need for broadband and tailored oxidation processes combined with other treatments, to remove transformation products and take advantage of multiple barriers. Mostly biological and/or adsorptive post-treatment after oxidation should be applied, because of their benefits for abatement of oxygenated DBPs and/or transformation products. The portfolio of oxidation processes should consider applications at various scales from municipal systems to single users and recognize the way that other water quality aspects (e.g., bromide) affect the performance. Research needs: Further development of electricity-driven processes, which avoid transport and storage of chemicals and are applicable at various scales. Furthermore, there is a need for improved engineering design to allow scaling up of these processes. Development of better models for activated carbon adsorption and further developments of computer-based prediction tools to assess biological transformation of disinfection byproducts and transformation products.

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OXIDATION PROCESSES: THE WAY FORWARD The dilemma of water treatment processes not being selective to specific target compounds is a severe limitation and a practical inevitability for oxidation processes. The ubiquitous matrix components reduce the treatment efficiency during oxidation and may lead to unintended consequences, such as disinfection byproducts. Furthermore, micropollutants are not removed during oxidation but transformed to a multitude of products. During sequential transformation processes, the concentration of individual transformation products decreases (oxidative dilution) but in some cases the transformation products are more toxic than the parent compounds. How do we guarantee that the risks of this approach do not outweigh the benefits? Unfortunately, the risk cannot be entirely eliminated, however, it can be minimized by a rigorous assessment approach. The following questions need to be addressed for an optimum application of oxidation processes. Will the Oxidation Process Achieve the Needed Decrease in Micropollutant Concentrations? Kinetics is key to the efficiency of an oxidation process. With existing knowledge, we can estimate oxidation kinetics, which is mostly sufficient to estimate the oxidative abatement efficiency in real systems. For novel oxidation processes, the overall energy demand and operating costs need to be similar or below benchmarked processes such as chlorination, ozonation or UVbased processes. The efficiency of novel processes tends to improve as technologies are further developed. For distributed treatment systems, a higher energy demand is justifiable, because no/minimal energy-intensive transport of water is required in these cases. Research needs: Further development of kinetics prediction tools based on quantum chemical computations for existing and emerging oxidation technologies. What Is the Risk of the Formation of Toxic Transformation Products? For certain oxidants and functional groups, transformation product formation can be assessed by computer-based prediction tools. A combination of these tools with advanced analytical methods allows the elucidation of transformation products and their potential toxicological consequences.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.8b00586. Additional information as noted in the text(PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Urs von Gunten: 0000-0001-6852-8977 Notes

The author declares no competing financial interest. F


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Photo provided by Urs von Gunten

Urs von Gunten is an environmental chemist, who has more than 25 years of experience in oxidative water and wastewater treatment processes. His main interests are in kinetic and mechanistic studies of oxidatively-induced transformation processes of micropollutants and the formation of disinfection by-products from matrix components and the ensuing (eco)toxicological consequences. Besides his academic activities, he emphasizes collaborations with practitioners from the water sector to transfer the findings of his research to real-world applications.

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ACKNOWLEDGMENTS I thank David Sedlak for many fruitful discussions and inspiring inputs during my sabbatical at UC Berkeley.

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